This disclosure relates generally to proton exchange membrane electrolysis cells, and, more particularly, to a membrane for use in such electrolysis cells.
Electrochemical cells are energy conversion devices that are usually classified as either electrolysis cells or fuel cells. Proton exchange membrane electrolysis cells can function as hydrogen generators by electrolytically decomposing water to produce hydrogen and oxygen gases. Referring to FIG. 1, a section of an anode feed electrolysis cell of the related art is shown at 10 and is hereinafter referred to as xe2x80x9ccell 10.xe2x80x9d Reactant water 12 is fed into cell 10 at an oxygen electrode (e.g., an anode) 14 where a chemical reaction occurs to form oxygen gas 16, electrons, and hydrogen ions (protons). The chemical reaction is facilitated by the positive terminal of a power source 18 connected to anode 14 and a negative terminal of power source 18 connected to a hydrogen electrode (e.g., a cathode) 20. Oxygen gas 16 and a first portion 22 of the water are discharged from cell 10, while the protons and a second portion 24 of the water migrate across a proton exchange membrane 26 to cathode 20. At cathode 20, hydrogen gas 28 is formed and is removed for use as a fuel. Second portion 24 of water, which is entrained with hydrogen gas, is also removed from cathode 20.
Another type of water electrolysis cell that utilizes the same configuration as is shown in FIG. 1 is a cathode feed cell. In the cathode feed cell, process water is fed on the side of the hydrogen electrode. A portion of the water migrates from the cathode across the membrane to the anode. A power source connected across the anode and the cathode facilitates a chemical reaction that generates hydrogen ions and oxygen gas. Excess process water exits the cell at the cathode side without passing through the membrane.
Electrolysis cell systems typically include one or more individual cells arranged in a stack, with the working fluids directed through the cells via input and output conduits formed within the stack structure. The cells within the stack are sequentially arranged, each including a cathode, a proton exchange membrane, and an anode (hereinafter xe2x80x9cmembrane electrode assemblyxe2x80x9d, or xe2x80x9cMEAxe2x80x9d). Each cell typically further comprises a first flow field in fluid communication with the cathode and a second flow field in fluid communication with the anode. The MEA may be supported on either or both sides by support members such as screen packs disposed within the flow fields, and which may be configured to facilitate membrane hydration and/or fluid movement to and from the MEA. Pressure pads or other compression means are often used to provide even compressive force from within the electrochemical cell.
Conventional electrolysis cells have been functionally limited by the lack of mechanical strength of conventional membranes, which rupture if subjected to excessive pressure, regardless of the efficacy of the flow fields. U.S. Pat. No. 5,547,551 to Bahar et al., which is incorporated herein in its entirety, discloses an ultrathin composite membrane comprising a base material and an ion exchange resin. Such membranes are conventionally used in fuel cells at very low membrane pressure differentials. There accordingly remains a need in the art for methods for operating an electrolysis cell at high pressure differentials (up to and exceeding about 10,000 pounds per square inch (psi) across the membrane without the conventional membrane damage associated with such high pressures.
The above-described drawbacks and disadvantages are alleviated by a method for the electrolysis of water, comprising applying a potential across an ultrathin composite membrane disposed between the first electrode and second electrode; introducing water to the ultrathin composite membrane through a first flow field in fluid communication with at least a portion of the first electrode; dissociating the water at the first electrode to form oxygen, protons, and electrons; moving the protons across the ultrathin composite membrane to the second electrode; and recombining the protons and the electrons at the second electrode to form hydrogen in a hydrogen flow field, at pressure differentials across the ultrathin composite membrane up to about 10,000 psi, or even higher.
In another embodiment, an electrolysis cell for the electrolysis of water comprises a first electrode; a second electrode; an ultrathin composite membrane disposed between and in intimate contact with the first electrode and the second electrode; a first flow field in fluid communication with the first electrode opposite the membrane; a second flow field in fluid communication with to the second electrode opposite the membrane; a water source in fluid communication with the first flow field; and hydrogen removal means in fluid communication with the second flow field.
The above described and other features are exemplified by the following figures and detailed description.